1. Technical Field of the Invention
The present invention relates in general to call connections in a telecommunications network, and in particular to saving dropped calls in the mobile telecommunications environment.
2. Description of Related Art
Because cellular telecommunications systems rely upon a radio interface for communications between a fixed base station and a mobile subscriber, failures or interruptions in the radio path between the base station and the mobile subscriber frequently result in dropped calls, wherein an ongoing call connection is eventually terminated because of an inability of the base station and mobile station to communicate with one another. In particular, if an ongoing call experiences a semi-permanent radio path failure (i.e., a radio path failure in which radio communications are interrupted for more than an inconsequential period of time), the mobile station and/or the cellular system will generally terminate the call connection. Such radio path failures can be due to, for example, broken base station equipment, a base station power outage, a transport network outage, software faults in the radio base station, or radio path disturbances.
One of the primary problems with dropped calls is that they inconvenience subscribers by requiring them to set up the call again, which can result in subscriber dissatisfaction. Furthermore, if dropped calls occur frequently enough, subscribers may be more reluctant to use their mobile telephones, effectively reducing the amount of revenues that the mobile telecommunication service provider generates.
In most cases, when a call is dropped, no effort is made to save the call connection. Instead, the subscriber must reinitiate the call. Some solutions for reconnecting involuntarily disconnected calls have been suggested. For example, Spear, U.S. Pat. No. 4,811,380, offers a solution to the problem of the mobile station not receiving a handoff message. In particular, when the system determines that a handoff from a first base site coverage area to a second base site coverage area is required, the first base site transmits the handoff message to the mobile station. If the mobile station does not receive the message, the mobile station determines that the call has been lost, seizes a signaling channel from the second base site, and requests a call re-connection via the second base site. The second base site informs the mobile station of the handoff instruction and the handoff is completed with a successful re-connection of the call. Spear, however, does not disclose how the mobile station locates the signaling channel for the second base site. Scanning for the appropriate signaling channel would require too much time. Therefore, the only option is for the mobile station to send the reconnect message on a signaling channel of a base site where the call was originally set up. However, in cases where one or more inter-base site handoffs have been performed, the mobile station is typically out of range of the original base site. Thus, Spear does not describe a feasible solution to the problem.
Alternatively, industry standard TIA/J-STD-034 describes a proposed solution for a connection of dropped emergency calls. This proposed solution, however, is network initiated and basically involves the network establishing a new connection with the mobile station by calling back the mobile station if the call is dropped. One of the main drawbacks of this proposed is solution is that, after the network detects that the connection to the mobile station has been lost, the network will have to wait until the mobile station becomes idle and returns to the control channel (i.e., when the subscriber pushes the xe2x80x9con-hookxe2x80x9d button on the mobile station) before it can initiate the call back procedure. Then, the mobile station can be paged as a normal terminating call, and the subscriber will receive a ring tone and have to manually answer the new call. An additional drawback of this proposed solution is that, if the mobile station is no longer within the same coverage area, the network probably will not be able to locate the mobile station to place the new call.
There is a need, therefore, for a method and system for reconnecting dropped calls in a mobile telecommunications network. Such a method and system would preferably allow a call connection to be reestablished promptly and without the need to manually initiate a new call. Furthermore, the method and system would allow for reconnection in cases where the mobile station has moved from one coverage area to another.
The present invention comprises a method and system for reconnecting dropped calls in a mobile telecommunications network. Upon detecting a call drop or loss of radio contact between a mobile station and a serving communication station, the mobile station sends a call reconnect request to the mobile telecommunications network. The call reconnect request is sent via a control channel of a target communication station, and in one embodiment of the invention, the control channel and/or its associated target communication station are selected from a neighboring cell list received by the mobile station. In response to the call reconnect request, the network reconnects the mobile station to the call using a radio channel of the target communication station.
In accordance with another embodiment of the invention, the call reconnection can be performed in situations in which the target communication station is associated with a target switching node that differs from a serving switching node associated with the serving communication station. Upon receiving the call reconnect request, the target switching node locates a switching node that is involved in the call by contacting a home location register for the mobile station and/or by contacting an anchor switching node for the call. The target switching node then requests a handoff of the call from the switching node involved in the call to the target switching node. Alternatively, the target switching node requests a handoff of the call from each of the border switching nodes. If one of the border switching nodes is currently serving the call, that border switching node hands off the call to the target switching node. Once the call is handed off to the target switching node, the mobile station can be reconnected with the call.